1. Field of the Invention
This invention relates to a data gathering system for use in an automotive vehicle for gathering data on engine operating variables and, more particularly, to such a system including an A/D converter.
2. Description of the Prior Art
A/D converters used in process control and measurement systems are designed to be operable with a sufficiently regulated power supply. In applications where such an A/D converter is used in an automotive vehicle for converting analog signals being indicative of various engine operating conditions into corresponding digital signals for application to the associated data processing unit, it is normally powered by a car battery exhibiting relatively large voltage drops at the start of actuation of the starting motor and electrical loads such as head lights. The battery voltage could drop to half the rated voltage if the ambient temperature is low or the car battery is dissipated.
Although the associated digital computer can be driven even when the battery exhibits such large voltage drops with the use of a power circuit designed to output a low regulated voltage, this results in limited sensor output voltage and limited A/D converter accuracy. Furthermore, errors are introduced in the A/D converter output due to battery voltage variations as well as offset and drift in the operational amplifier of the A/D converter.